This invention relates to infrared sources and more particularly infrared sources having increased electrical resistance.
There are certain equipments which use electrically heated graphite source to generate large amounts of infrared energy. These equipments include a graphite source enclosed within a transparent envelope such as a quartz window. These sources are often used in equipment where the voltage available to power the sources is fixed. Presently such sources are configured as cylindrical hollow rods. Because of the high temperatures at which such rods operate, usually on the order of 2000.degree. K., the lifetime of such sources are limited. Generally deterioration of the sources occur by having the graphite evaporate at the very high operating temperatures and deposit on the surfaces of the enclosing transparent window, thereby decreasing the transmissivity thereof.
It is desirable to have these sources operate at lower temperatures while radiating at the same or greater power levels. This source temperature reduction can be accomplished in two ways - improving the emission characteristics of the radiating surface and increasing the radiating surface area.
This source material is not a perfect radiator, and therefore, some emission improvement is realizable.
The increase in radiating surface area may be obtained by increasing either the length or the outer diameter of the cylindrical rod. Increasing the length of the rod is impractical because if the rods are configured to fit within certain equipment having a defined size, increasing the length of the rod will cause a like increase in the size of the equipment. Therefore, such rods could not be used in currently configured equipment.
Increasing the outer diameter of the rod requires a compensating increase of the resistance. This, of course, can be done by either increasing the resistivity, increasing the length or decreasing the cross-sectional area. It is impractical to increase the resistivity since this requires a change in materials and there are very few materials which operate at the desired temperatures on the order of 2000.degree. K. As stated before, increasing the length is impractical.
The third alternative is to decrease the cross-sectional area, by making the walls of the hollow cylindrical rods thinner. This is also undesirable since the structural integrity of the source will be severely affected.
Accordingly, it is an object of this invention to provide an improved infrared source.
It is a further object of this invention to provide an improved infrared source having higher emissivity.